Separation of a target substance from a fluid or mixture using encapsulated sorbents

ABSTRACT

Method and apparatus for separating a target substance from a fluid or mixture. Capsules having a coating and stripping solvents encapsulated in the capsules are provided. The coating is permeable to the target substance. The capsules having a coating and stripping solvents encapsulated in the capsules are exposed to the fluid or mixture. The target substance migrates through the coating and is taken up by the stripping solvents. The target substance is separated from the fluid or mixture by driving off the target substance from the capsules.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of pending application Ser. No.13/321,418, filed Dec. 6, 2011, which claims benefit under 35 U.S.C.§119(e) of U.S. Provisional Patent Application No. 61/444,461 filed Feb.18, 2011 entitled “carbon dioxide separation using encapsulatedsorbents, the disclosure of which is hereby incorporated by reference inits entirely for all purposes.

U.S. patent application Ser. No. 12/783,394 filed May 19, 2010 by RogerD. Aines, one of inventors in the present application, for CatalystFunctionalized Buffer Sorbent Pebbles for Rapid Separation of CarbonDioxide from Gas Mixtures discloses systems related to the presentinvention. U.S. patent application Ser. No. 12/784,665 filed May 21,2010 by Roger D. Aines, William L. Bourcier, and Brian Viani; Roger D.Aines and William L. Bourcier being inventors in the presentapplication; for Slurried Solid Media for Simultaneous WaterPurification and Carbon Dioxide Removal from Gas Mixtures disclosessystems related to the present invention. The disclosures of U.S. patentapplication Ser. No. 12/783,394 filed May 19, 2010 and U.S. patentapplication Ser. No. 12/784,665 filed May 21, 2010 are incorporatedherein in their entirety for all purposes by this reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the United States Department ofEnergy and Lawrence Livermore National Security, LLC for the operationof Lawrence Livermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to removal of substances from fluids ormixtures and more particularly to removal of a target substance from afluid or mixture.

2. State of Technology

The article “carbon Dioxide into the Briny Deep” in the October 2010issue of Science and Technology Review provides the state of technologyinformation reproduced below.

WITH every passing year, the amount of carbon dioxide (CO₂) in theatmosphere increases. Because of the way this gas absorbs and emitsinfrared radiation, excessive quantities can cause the warming ofEarth's atmosphere. Natural sources of atmospheric CO₂ such as volcanicoutgassing, the combustion of organic matter, and the respirationprocesses of living aerobic organisms are nearly balanced by physicaland biological processes that remove the gas from the atmosphere. Forexample, some CO₂ dissolves in seawater, and plants remove some byphotosynthesis.

However, problems arise with the increased amounts of CO₂ from humanactivities, such as burning fossil fuels for heating, power generation,and transport as well as some industrial processes. Natural processesare too slow to remove these anthropogenic amounts from the atmosphere.In 2008, 8.67 gigatons of carbon (31.8 gigatons of CO₂) were releasedworldwide from burning fossil fuels, compared with 6.14 gigatons in1990.

The present level of atmospheric CO₂ is higher than at any time duringthe last 800,000 years and likely is higher than it has been in the last20 million years. Researchers around the world are exploring ways todispose of this excess. One proposed approach, called carbon capture andsequestration, is to store CO₂ by injecting it deep into the ocean orinto rock formations far underground. The G8, an informal group ofeconomic powers including the U.S., has endorsed efforts to demonstratecarbon capture and sequestration. The international forum recommendedthat work begin on at least 20 industrial-scale CO₂ sequestrationprojects, with the goal of broadly deploying the technology by 2020.

Several carbon sequestration projects are already under way. One, underthe North Sea, is part of an oil drilling operation that separates CO₂from natural gas and traps it in undersea rock formations. Otherprojects are using sequestered CO₂ to push oil around underground sothat drillers can maximize the quantity of crude oil they remove—aprocess called enhanced oil recovery.

An alternative approach, being pursued by researchers at LawrenceLivermore and the Department of Energy's National Energy TechnologyLaboratory, involves putting CO₂ back into the ground whilesimultaneously producing freshwater. According to Livermore geochemistRoger Aines, who leads the Laboratory's work on this project, vastunderground sandstone formations are filled with very salty water, manytimes saltier than the ocean. The idea is to pump CO₂ into these rockformations, thereby pushing briny water up into a reverse-osmosiswater-treatment plant where most of the salt can be removed. The resultis to increase volume for storing CO₂ in the underground formation whileproducing freshwater aboveground.

Although this water might be too salty to drink, it would provide acritical resource for industrial processes that require huge quantitiesof freshwater. Petroleum refining, for example, consumes 1 to 2 billiongallons of water per day. Even technologies designed to reducegreenhouse gases, such as the biofuels production process, areincreasing demands on the world's water resources.

United States Published Patent Application No. 2007/0169625 by Roger D.Aines and William L. Bourcier for a carbon ion pump for removal ofcarbon dioxide from combustion gas and other gas mixtures provides thestate of technology information described below.

-   -   Carbon dioxide makes up from 5% (modern gas-fired plants) to 19%        (modern coal plants) of the flue gas from a power plant. The        remainder is mostly nitrogen, unused oxygen, and oxides of        nitrogen and sulfur (which are strong greenhouse gases in        addition to contributing to poor quality). A major limitation to        reducing greenhouse gases in the atmosphere is the expense of        stripping carbon dioxide from other combustion gases. Without a        cost-effective means of accomplishing this, the worlds        hydrocarbon resources, if used, will continue to contribute        carbon dioxide to the atmosphere.

The disclosure of United States Published Patent Application No.2007/0169625 is incorporated herein in its entirety for all purposes.

United States Published Patent Application No. 2007/0170060 by WilliamL. Bourcier, Roger D. Aines, Jeffery, J. Haslam, Charlene, M. Schaldach,Kevin, C. O'Brien, and Edward Cussler for a deionization anddesalination using electrostatic ion pumping provides the state oftechnology information described below.

-   -   The present invention provides for a method and system (e.g., a        desalination system and method) that utilizes synchronized        externally applied electrostatic fields in conjunction with an        oscillating fluid flow to immobilize and separate ions from        fluids. While salt ion removal from water is a preferred        embodiment, it is to be understood that other ions can also be        beneficially removed from fluids, as disclosed herein by the        apparatus/systems and methods of the present invention. The ion        pump separates any non-ionic liquid, from ionic impurities        contained within that liquid. The present invention may        therefore be used to purify either the liquid, as in the case of        water, or the salts. One outlet stream has liquid reduced in        salt content, and the other side it is increased and this side        is useful if the valuable product is the salt, and not the        fluid. In addition, many drugs are inherently ionic chemicals        that can be separated by the methods disclosed herein from a        liquid in which they have been created. As another beneficial        embodiment, the methods and apparatus/system can be configured        to separate valuable minerals, such as, but not limited to        lithium. Conventionally, the separation of ions and impurities        from electrolytes has been achieved using a variety of processes        including: ion exchange, reverse osmosis, electro dialysis,        electrodeposition and filtering. In conventional reverse osmosis        systems, for example, water is forced through a membrane, which        acts as a filter for separating the ions and impurities from        water. Reverse osmosis systems require significant energy to        move the water through the membrane. The flux of water through        the membrane results in a considerable pressure drop across the        membrane. This pressure drop is responsible for most of the        energy consumption by the process. The membrane also degrades        with time, requiring the system to be shut down for costly and        troublesome maintenance.

The disclosure of United States Published Patent Application No.2007/0169625 is incorporated herein in its entirety for all purposes.

United States Published Patent Application No. 2010/0300287 by Roger D.Aines, William L. Bourcier, and Brian Viani for slurried solid media forsimultaneous water purification and carbon dioxide removal from gasmixtures provides the state of technology information described below.

-   -   Most industrial process for separating CO₂ from gas mixtures        utilize water as the primary separation media. This is because        water provides an extremely large factor to separated carbon        dioxide from non-ionizable nitrogen and oxygen. In those        processes, the water contains additives that serve to buffer the        carbonic acid that forms upon CO₂ dissolution, and also to speed        the CO₂ dissolution process. Typically those additives are        amines although in some processes hydroxides (such as NaOH) are        used.

The disclosure of United States Published Patent Application No.2010/0300287 is incorporated herein in its entirety for all purposes.

United States Published Patent Application No. 2010/0303694 by Roger D.Aines for catalyst functionalized buffer sorbent pebbles for rapidseparation of CO₂ from gas mixtures provides the state of technologyinformation described below.

-   -   Most industrial process for separating CO₂ from gas mixtures        utilize water as the primary separation media. This is because        water provides an extremely large factor to separated carbon        dioxide from non-ionizable nitrogen and oxygen. In those        processes, the water contains additives that serve to buffer the        carbonic acid that forms upon CO₂ dissolution, and also to speed        the CO₂ dissolution process. Typically those additives are        amines although in some processes hydroxides (such as NaOH) are        used.

The disclosure of United States Published Patent Application No.2010/0300287 is incorporated herein in its entirety for all purposes.

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

The present invention provides a system for the removal of a targetsubstance from a fluid or mixture. Capsules having a coating andstripping material encapsulated in the capsules are provided. Thecoating is permeable to the target substance. The capsules having acoating and stripping material encapsulated in the capsules are exposedto the fluid or mixture. The target substance migrates through saidcoating and is taken up by the stripping material. The target substanceis removed from the fluid or mixture by driving off the target substancefrom the capsules. The target material that has been removed can besold, stored, sequestered, or otherwise disposed of.

The present invention has use in any application where a targetsubstance needs to be removed from a fluid or mixture. For example, thepresent invention has use in the capture of carbon dioxide from gasmixtures containing carbon dioxide (examples: fossil fuel plants,natural gas streams, air). Also, the present invention has use inremoving and/or capturing other gases including nitrous oxides (NOx),sulphates (SOx), hydrogen sulfide, or other trace gases thatpreferentially dissolve in a liquid for removal. In addition the presentinvention has use for producing products for the pharmaceutical,chemical, energy, food, coatings, cosmetic, and other industries.

In one embodiment, the present invention provides an apparatus andmethod for separating carbon dioxide from a gas mixture that includescarbon dioxide. Capsules having a polymer coating and stripping solventsencapsulated in the capsules are provided. The polymer coating ispermeable to carbon dioxide. The polymer coated capsules are exposed tothe gas mixture that includes carbon dioxide. The carbon dioxidemigrates through the polymer coating of the capsules and is taken up bythe stripping solvents. The carbon dioxide is separated from the gasmixture by driving off the carbon dioxide from the polymer coatedcapsules. This may be accomplished by heating the polymer coatedcapsules. For example, steam can be directed onto the polymer coatedcapsules to drive off the carbon dioxide from the capsules. The carbondioxide that has been separated from the gas mixture can be sold,stored, sequestered, or otherwise disposed of.

Many industrial carbon dioxide separation schemes utilize water as theprimary separation media, with additives such as amine compounds toincrease the rate or capacity. This is because water provides anextremely large factor to separate carbon dioxide from non-ionizablenitrogen and oxygen. Once the CO₂ dissolves in water, it is now a verydifferent molecule than oxygen and nitrogen, with concordant highseparation efficiency.

The present invention provides a system for water based removal ofcarbon dioxide by encapsulating CO₂ stripping solvents in polymers. Thecapsules that are produced contain solvent or solvent mixtures that canbe freely tailored to the feed stream to optimize CO₂ loading, minimizethe heat for regeneration, lower the heat of mixing, and limit the fluxof corrosive by-products into a stripping tower. Sorbents may bemixtures of amines, or inorganic bases and carbonates, ammonia, ionicliquids, or alkaline solid-liquid slurries. The present inventionoptionally incorporates enzymes or catalysts to enhance the rate of CO₂hydration and increase the rate of uptake. The present invention enablesbetter heat cycle performance and reduces solvent loss during processingwhen compared to conventional amine stripping technologies.

The present invention provides a system for separating carbon dioxidefrom a gas mixture. The gas mixture and the carbon dioxide are dissolvedin water providing water with the dissolved gas and carbon dioxide.Capsules having a polymer coating and stripping solvents encapsulated inthe capsules are produced for separating the carbon dioxide. Thecapsules containing the stripping solvents are exposed to the gas andcarbon dioxide. The carbon dioxide migrates through the polymer coatingand is taken up by the stripping solvents. The carbon dioxide isseparated by driving off the carbon dioxide from the capsules usingheat, chemical exchange, or other chemical processes.

The present invention provides the effective use of catalysts to open upa new range of process conditions and methods for industrial CO₂capture, ranging from near-term improvement of existing processes, tolonger term enablement of a new process where the working solvent isencapsulated in a polymer coat, minimizing corrosion and solventdegradation problems while greatly reducing the total energy requirementby reducing the water content of the solvent.

The encapsulation of amines within a spherical polymer shell inaccordance with the present invention has advantages over conventionalamine capture systems. First, isolating the amines within the polymershell can reduce degradation of the solvent and confine any degradationproducts to the capsule, thereby reducing corrosion of the capturesystem. This allows for higher concentrations of solvent and thus higherloadings of CO₂, reducing the energy needed for regeneration, andpermits batches of solvent to have a longer lifetime before they must beremoved due to degradation product buildup. Second, encapsulation allowsnovel process designs. For example, a capture system based onencapsulated amines may look like a fluidized bed as opposed to aconventional packed tower. The beads can be agitated either by the fluegas or stripping gas, and run as a batch process. Third, encapsulationenforces a high surface area per volume of solvent, improving theperformance particularly of viscous stripping solvents which may be hardto use in conventional applications. This new process concept takesadvantage of the encapsulation during the regeneration step by all thesame advantages previously cited, and also by permitting a strippingusing heat transfer media that have a lower boiling point and heat ofvaporization than water (e.g. methanol) or a lower water pressure suchas hot oil. Such alternative methods cannot be used with exposed aminesolution, but in an encapsulated system they would enable higher orlower-temperature regeneration, reducing the capital cost and energyrequirements of operating the stripper under vacuum or permittingrecovery of carbon dioxide at very high pressure, reducing thesubsequent cost of compression required for storage or transport.

The present invention provides benefits in fabrication andmanufacturability. The beads can be fabricated at a size small enoughfor efficient mass transfer and large enough for ease of handling. Thepresent invention provides methods to fabricate liquid filled shells inthe size range of 100 microns to 1 mm with wall thickness from 5-10microns.

The present invention provides benefits in survivability and robustness.The present invention identifies several polymers that can withstandtypical regeneration temperatures of 100-150 C. In addition, theselected polymers will be capable of withstanding small volumetricchanges due to absorption desorption of CO₂ and water Applicants havedetermined from data on the densities of common CO₂ solvents thatloading and unloading cycles will not cause a volume increase such thatthe capsule is likely to burst.

Applicants have also determined that mass transport of otherconstituents in the gas and sorbent will not significantly interferewith CO₂ capture. Water will tend to diffuse through the capsule walldepending on concentration and pressure gradients and their directions.The vapor pressure of water outside the capsule during loading will bethat of the flue gas, which varies with fuel and process type, but isgenerally around 10% by volume. The water vapor pressure surrounding thecapsule is therefor expected to be around 0.1 bars. The partial pressure(fugacity) of water inside the capsule will depend on the relativeproportions of water, amine and CO₂, but is typically also around 0.1bats. No significant mass transport of water into or out of the capsuleis anticipated in an amine-water system. A feature of system is that thewater in the capture solvent can be adjusted to be equal to the partialpressure of water for a given flue gas to be used as a CO₂ source. Watertransfer into other solvents (carbonates, ionic liquids) can beaccommodated by slight changes in size of the polymer. The polymersunder consideration are sufficiently elastic to permit changes in sizeof +/−10% typically.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 is a pictorial illustration of a system for separating carbondioxide from gas mixtures.

FIG. 2 illustrates an embodiment of one of the capsules shown in FIG. 1.

FIG. 2 illustrates an embodiment of a system for separating carbondioxide from gas mixtures.

FIG. 3 illustrates another embodiment of a system for separating carbondioxide from gas mixtures.

FIG. 4 illustrates yet another embodiment of a system for separatingcarbon dioxide from gas mixtures.

FIG. 5 illustrates yet another embodiment of a system for separatingcarbon dioxide from gas mixtures.

FIGS. 6A and 6B illustrate another embodiment of a system for separatingcarbon dioxide from gas mixtures.

FIG. 7 illustrates a system for making polymer coated capsules.

FIG. 8 illustrates use of catalysts and polymer additives to improvecapsule performance.

FIG. 9 illustrates flue gas (e.g., CO₂, H₂O, N₂, SO_(x), NO_(x)) and/orother gas mixtures being processed by passing it upwards through aabsorption tower while being contacted with a suspension of polymercoated capsules.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring to the drawings, to the following detailed description, and toincorporated materials, detailed information about the invention isprovided including the description of specific embodiments. The detaileddescription serves to explain the principles of the invention. Theinvention is susceptible to modifications and alternative forms. Theinvention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

The present invention provides a system for the removal of a targetsubstance from a fluid or mixture. The system has use in any applicationwhere a target substance needs to be removed from a fluid or mixture.For example, has use in processing system for producing products for thepharmaceutical, chemical, energy, food, coatings, cosmetic, and otherindustries. Also, the system has use in the capture of carbon dioxidefrom gas mixtures containing carbon dioxide (examples: fossil fuelplants, natural gas streams, air). The system has use in removing and/orcapturing other gases including nitrous oxides (NOx), sulphates (SOx),hydrogen sulfide, or other trace gases that preferentially dissolve in aliquid for removal. In the system of the present invention, capsuleshaving a coating and stripping material encapsulated in the capsules areprovided. The coating is permeable to the target substance. The capsuleshaving a coating and stripping material encapsulated in the capsules areexposed to the fluid or mixture. The target substance migrates throughsaid coating and is taken up by the stripping material. The targetsubstance is removed from the fluid or mixture by driving off the targetsubstance from the capsules. The target material that has been removedcan be sold, stored, sequestered, or otherwise disposed of.

The present invention provides an apparatus and method for separatingcarbon dioxide from a gas mixture including carbon dioxide. Capsuleshaving a polymer coating and stripping solvents encapsulated in thecapsules are provided. The polymer coating is permeable to carbondioxide. The polymer coated capsules are exposed to the gas mixture thatincludes carbon dioxide. The carbon dioxide migrates through the polymercoating of the capsules and is taken up by the stripping solvents. Thecarbon dioxide is separated from the gas mixture by driving off thecarbon dioxide from the polymer coated capsules. This may beaccomplished, for instance, by heating the polymer coated capsules. Forexample, steam can be directed onto the polymer coated capsules to driveoff the carbon dioxide from the capsules. The carbon dioxide that hasbeen separated from the gas mixture can be sold, stored, sequestered, orotherwise disposed of.

Many industrial carbon dioxide separation schemes utilize water as theprimary separation media, with additives such as amine compounds toincrease the rate or capacity. This is because water provides anextremely large factor to separate carbon dioxide from non-ionizablenitrogen and oxygen. Buffer compounds are fundamentally required to keepthe water solution in the correct pH region for the conversion of CO₂ tocarbonate or bicarbonate ions.

The present invention provides a system for removal and concentration ofcarbon dioxide by encapsulating CO₂ stripping solvents in polymers. Thecapsules that are produced contain solvent or solvent mixtures that canbe freely tailored to the feed stream to optimize CO₂ loading, minimizethe heat for regeneration, lower the heat of mixing, and limit the fluxof corrosive by-products into a stripping tower. Sorbents may bemixtures of amines, or inorganic bases, or alkaline solid-liquidslurries. The present invention optionally incorporates enzymes orcatalysts to enhance the rate of CO₂ hydration and increase the rate ofuptake. The present invention enables better heat cycle performance andreduces solvent loss during processing when compared to conventionalamine stripping technologies.

Referring now to the drawings and in particular to FIG. 1, an embodimentof a system for separating carbon dioxide from gas mixtures isillustrated. The system for separating carbon dioxide from gas mixturesis designated generally by the reference numeral 100. As illustrated inFIG. 1 a flue gas 102 is bubbled through a slurry of water 104 andcapsules 106. Water is optional in the process but is always present influe gas, even if not in liquid form.

The capsules include a polymer coating and stripping solventsencapsulated within the capsules 106. The polymer surface layer ispermeable to carbon dioxide. The stripping solvents encapsulated withinthe capsule can be any or a mixture of the following primary, secondary,tertiary, and hindered amines, caustic solutions, ionic buffersolutions, ionic liquids, ammonia, and other solvents having high asolubility of carbon dioxide.

Carbon dioxide is absorbed by passing the flue gas 102 from which thecarbon dioxide is to be separated through the slurry made up of water104 and the capsules 106. The carbon dioxide migrates through thepolymer coating of the capsules 106 and is taken up by the strippingsolvents. The carbon dioxide is separated by driving off the carbondioxide from the capsules. The carbon dioxide can be transported to aninjection site for sequestration and long-term storage in any of avariety of suitable geologic formations.

Referring now to FIG. 2, an embodiment of one of the capsules shown inFIG. 1 is illustrated in greater detail. The capsule is designatedgenerally by the reference numeral 200. The capsule 200 includes apolymer coating 202 and stripping solvents 204 encapsulated within thecapsule 200. The capsule 200 is 200 to 500 microns in diameter.

The polymer surface layer 202 is optimally less than 10 microns thickand is very permeable to carbon dioxide. The polymer surface layer 202is made of any of several families of polymers, including polystyrene,polyethylene, polypropylene, nylon, and others.

The stripping solvents 204 encapsulated within the capsule 200 can beany or a mixture of the following: primary, secondary, tertiary, andhindered amines, caustic solutions, ionic buffer solutions, ammonia,ionic liquids, and other solvents having high a solubility of carbondioxide.

The capsules are used to capture carbon dioxide from gas mixtures. Thecontacting device can be one of several configurations including afluidized bed, a countercurrent flow, suspended in an aqueous liquid,etc. After loading, the capsules are typically regenerated thermally ina controlled environment where the carbon dioxide is released in pureform suitable for compression and injection into the subsurface. Theenvironment could be that of steam at a partial pressure such that is itin equilibrium with water inside the capsules to prevent water transportinto or out of the capsule. Dry heat from an heat exchanger or oil bathcould optionally be used at this stage.

The present invention provides the effective use of catalysts to open upa new range of process conditions and methods for industrial CO₂capture, ranging from near-term improvement of existing processes, tolonger term enablement of a new process where the working solvent isencapsulated in a polymer coat, minimizing corrosion and solventdegradation problems while greatly reducing the total energy requirementby reducing the water content of the solvent.

The encapsulation of amines within a spherical polymer shell inaccordance with the present invention has advantages over conventionalamine capture systems. First, isolating the amines within the polymershell can limit degradation of the solvent and prevent migration of anydegradation products formed, thereby reducing corrosion of the capturesystem. This allows for higher concentrations of solvent and this higherloadings of CO, reducing the energy needed for regeneration. Equipmentmay be smaller and constructed out of less expensive materials, forinstance carbon steel in place of stainless steel, when the corrosionproducts are contained within the capsules and unable to read with thecapture device. Second, encapsulation allows novel process designs. Forexample, a capture system based on encapsulated amines may look like afluidized bed as opposed to a conventional packed tower. The beads canbe agitated either by the flue gas (or stripping gas) or run as a batchprocess. This new process concept can take advantage of theencapsulation during regeneration by using a stripping that has a lowerboiling point and heat of vaporization than water (e.g. methanol). Suchalternative gases cannot be used with exposed amine solution, but in anencapsulated system they would enable lower-temperature regenerationwithout the capital cost and energy requirements of operating thestripper under vacuum.

The present invention provides benefits in fabrication andmanufacturability. The beads can be fabricated at a size small enoughfor efficient mass transfer and large enough for ease of handling. Thepresent invention provides methods to fabricate liquid filled shells inthe size range of 100 microns to 1 mm with wall thickness from 5-10microns.

The present invention provides benefits in survivability and robustness.The present invention identifies several polymers that can withstandtypical regeneration temperatures of 100-120 C. In addition, theselected polymers will be capable of withstanding small volumetricchanges due to absorption desorption of CO₂ and water. Applicants havedetermined from data on the densities of common CO₂ solvents thatloading and unloading cycles will not cause a volume increase such thatthe capsule is likely to burst.

The capsule 200 shown in FIG. 2 can be used to illustrate otherembodiments of the present invention. The capsule 200 is illustrative ofa system utilizing capsules having a coating 202 and stripping material204 encapsulated in the capsules that capture a target substance in afluid or mixture. The coating 202 is permeable to the target substanceand the target substance migrates through said coating 202 and is takenup by the stripping material 204. The target substance is capture bydriving off the target substance from the capsule 200 thereby separatingthe target substance from the fluid or mixture.

In one embodiment the coating 202 is made of a porous solid. In anotherembodiment the coating 202 includes carbon fibers. In yet anotherembodiment the coating 202 includes carbon nanotubes. The carbonnanotubes can be used to provide strength and resilience to the capsule200. The carbon nanotubes can aligned to improve and controlpermeability of the coating 202. In another embodiment the coating 202is made of any of several families of polymers, including polystyrene,polyethylene, polypropylene, and nylon. The surface layer 202 isoptimally less than 10 microns thick and is very permeable to the targetsubstance.

In one embodiment the stripping solvents 204 encapsulated within thecapsule 200 can be primary, secondary, tertiary, and hindered amines,caustic solutions, ionic buffer solutions, ammonia, or other solventshaving solubility of carbon dioxide encapsulated in the capsules. Inanother embodiment the stripping solvents 204 encapsulated within thecapsule 200 can be nitrous oxide wherein the nitrous oxide migratesthrough the coating 202 and is taken up by the stripping material 204.In yet another embodiment the stripping solvents 204 encapsulated withinthe capsule 200 can be sulphates wherein the sulphates migrate throughthe coating 202 and are taken up by the stripping material 204. Inanother embodiment the stripping solvents 204 encapsulated within thecapsule 200 can be hydrogen sulfide wherein the hydrogen sulfidemigrates through the coating 202 and is taken up by the strippingmaterial 204.

The present invention is further explained by a number of examples. Theexamples further illustrate Applicants' system for separating carbondioxide from a gas mixture. In the examples, the gas mixture and thecarbon dioxide are dissolved in water providing water with the dissolvedgas and carbon dioxide. The capsules have a polymer coating andstripping solvents encapsulated within the capsules. The capsulescontaining the stripping solvents are exposed to the water with thedissolved gas and carbon dioxide. The carbon dioxide migrates throughthe polymer coating and is taken up by the stripping solvents. Thecarbon dioxide is separated by driving off the carbon dioxide from thecapsules.

Example 1

In example 1, a system for carbon dioxide removal from gas mixtures isdescribed and illustrated. Example 1 is illustrated by FIG. 3 showing amethod of separating CO₂. The method is designated generally by thereference numeral 300. The steps of the method 300 are described below.

Method Steps—FIG. 3

Step 1 (Reference Numeral 302)—Flue gas (e.g., CO₂, H₂O, N₂SO_(x),NO_(x)) and/or other gas mixtures 301 is processed in a water wash 303.The system/process 300 is thus designed to dissolve flue gas and/orother gas mixtures first in slightly alkaline water as introduced by thewater wash 303 prior to producing a concentrate from which a harvestedCO₂ can be produced. The water wash 303 system itself can beincorporated from known systems utilized by those of ordinary skill inthe art. As an illustration only, the common system can include aplurality of spray levels to inject the liquid so as to contact the fluegas, which is designed to flow through such a water wash 303 at apredetermined constant velocity. The number of spray levels can bevaried depending on the effective liquid to gas (L/G) ratios. Inaddition, spray nozzles of different sizes producing different flowrates, spray patterns, and droplet sizes can also be utilized.

Step 2 (Reference Numeral 304)—The water containing the flue gas passesfrom water wash 303 to an area wherein capsules 305 are added forming aslurry 307 of water, capsules 305, CO₂, and the impurities. Carbondioxide is absorbed by passing the gas from which the carbon dioxide isto be separated through the slurry 307 either by bubbling, use of anabsorber tower, or any other means suitable for absorbing a gas into aliquid. The process for absorbing carbon dioxide or other acid gases issimilar to the process used in amine stripping.

The mixed gas is passed through or over a solution of the watercontaining the capsules 305. The water is any water which is desired tobe purified during the desorption step. This can be seawater, brine,water compromised by any low-volatility salt or other dissolvedcomponent. The water can also be a process fluid that is 100% recycled(not purified) during the desorption stage, but this is less thanoptimal. The CO₂ or other acid gases dissolve in the water and are thenabsorbed by the capsules 305, permitting more to dissolve into the wateruntil saturation is reached.

Step 3 (Reference Numerals 308, 309, 310, & 311)—The mixture of capsulescontaining the CO₂ is then heated 309 to the boiling point of water(typically 100.degree. C.) to release the CO₂ from the capsules 305.During the heating 309 step steam 311 is produced. In order to desorbthe carbon dioxide much lower temperatures are required than if the sameamines are used free in solution. Carbon dioxide is freely evolved atslightly below 100 degree C. in pure water. This is because there isrelatively little carbon dioxide gas in the water (it's partial pressure(fugacity) is lower).

Step 4 (Reference Numerals 312 & 313)—The steam 311 is condensed bycooling 313.

Step 5 (Reference Numerals 314 & 315)—Condensing of the steam 311produces fresh water 315. With a buffer media that is easily separable(by filtration) from the working liquid medium, it is now possible touse a brine or other compromised water as the feedstock. During theregeneration step the steam which must necessarily be produced can becondensed as fresh water obtaining dual benefit for the energy requiredto regenerate the CO₂. None of the buffer material carries over into thedistillate unlike the fairly volatile amines currently used. Mostimportantly, as the undesirable components of the process water (forinstance salt) build up in the bottom of the distilling process, theymay periodically be removed and the buffer material easily filtered outfrom the rejected components for return to the process. This cannot bedone easily with any of the dissolved buffer materials currently in use.One advantage is longer buffer life by reduced temperatures andisolation of the buffer material from oxygen.

Step 6 (Reference Numerals 316 & 319)—Condensing of the steam 311purifies the gas stream coming out of the process to nearly pure CO₂319. The CO₂ 319 can be used or sequestered. The CO₂ 319 can betransported to an injection site for sequestration and long-term storagein any of a variety of suitable geologic formations.

Example 2

In example 2, a system for simultaneous water purification and carbondioxide removal from gas mixtures is described and illustrated. Example2 is illustrated by the method illustrated in FIG. 4. The method isdesignated generally by the reference numeral 400. The steps of themethod 400 are described below.

Method Steps—FIG. 4

Step 1 (Reference Numeral 402)—Flue gas (e.g., CO₂, H₂O, N₂SO_(x),NO_(x)) and/or other gas mixtures 401 is processed in a water wash 403.The system/process 400 is thus designed to dissolve flue gas and/orother gas mixtures first in slightly alkaline water as introduced by thewater wash 403 prior to producing a concentrate from which a harvestedCO₂ can be produced. The water wash 403 system itself can beincorporated from known systems utilized by those of ordinary skill inthe art. As an illustration only, the common system can include aplurality of spray levels to inject the liquid so as to contact the fluegas, which is designed to flow through such a water wash 403 at apredetermined constant velocity. The number of spray levels can bevaried depending on the effective liquid to gas (L/G) ratios. Inaddition, spray nozzles of different sizes producing different flowrates, spray patterns, and droplet sizes can also be utilized.

Step 2 (Reference Numeral 404)—The water containing the flue gas passesfrom water wash 403 to an area wherein capsules 405 are added forming aslurry 407 of water, capsules 405, CO₂, and the impurities. Carbondioxide is absorbed by passing the gas from which the carbon dioxide isto be separated through the slurry 407 either by bubbling, use of anabsorber tower, or any other means suitable for absorbing a gas into aliquid. The process for absorbing carbon dioxide or other acid gases issimilar to the process used in amine stripping.

The mixed gas is passed through or over a solution of the watercontaining the capsules 405. The water is any water which is desired tobe purified during the desorption step. This can be seawater, brine,water compromised by any low-volatility salt or other dissolvedcomponent. The water can also be a process fluid that is 100% recycled(not purified) during the desorption stage, but this is less thanoptimal. The CO₂ or other acid gases dissolve in the water and are thenabsorbed by the capsules 405, permitting more to dissolve into the wateruntil saturation is reached.

Step 3 (Reference Numerals 408, 409, 410, & 411)—The mixture of capsulescontaining the CO₂ is then heated 409 to the boiling point of water(typically 100.degree. C.) to release the CO₂ from the capsules 405.During the heating 409 step steam 411 is produced. In order to desorbthe carbon dioxide much lower temperatures are required than if the sameamines are used free in solution. Carbon dioxide is freely evolved atslightly below 100 degree C. in pure water. This is because there isrelatively little carbon dioxide gas in the water (it's partial pressure(fugacity) is lower).

Step 4 (Reference Numerals 412 & 413)—The steam 411 is condensed bycooling 413.

Step 5 (Reference Numerals 414 & 415)—Condensing of the steam 411produces fresh water 415. With a buffer media that is easily separable(by filtration) from the working liquid medium, it is now possible touse a brine or other compromised water as the feedstock. During theregeneration step the steam which must necessarily be produced can becondensed as fresh water obtaining dual benefit for the energy requiredto regenerate the CO₂. None of the buffer material carries over into thedistillate unlike the fairly volatile amines currently used. Mostimportantly, as the undesirable components of the process water (forinstance salt) build up in the bottom of the distilling process, theymay periodically be removed and the buffer material easily filtered outfrom the rejected components for return to the process. This cannot bedone easily with any of the dissolved buffer materials currently in use.One advantage is longer buffer life by reduced temperatures andisolation of the buffer material from oxygen.

Step 6 (Reference Numerals 416 & 417)—Condensing of the steam 411purifies the gas stream coming out of the process to nearly pure CO₂417. The CO₂ 417 can be used or sequestered. The CO₂ 417 can betransported to an injection site for sequestration and long-term storagein any of a variety of suitable geologic formations.

Step 7 (Reference Numerals 416 & 417)—Condensing of the steam 411 withremoval of the CO₂ 417 and water 415 leaves water with impurities 419.

Example 3

In example 3, a system for simultaneous water purification and carbondioxide removal from gas mixtures is described and illustrated. Example3 is illustrated by the method illustrated in FIG. 5. The method isdesignated generally by the reference numeral 500. The steps of themethod 500 are described below.

Method Steps—FIG. 5

Step 1 (Reference Numeral 502)—Flue gas (e.g., CO₂, H₂O, N₂SO_(x),NO_(x)) and/or other gas mixtures 501 is processed in a water wash 503.The system/process 500 is thus designed to dissolve flue gas and/orother gas mixtures first in slightly alkaline water as introduced by thewater wash 503 prior to producing a concentrate from which a harvestedCO₂ can be produced. The water wash 503 system itself can beincorporated from known systems utilized by those of ordinary skill inthe art. As an illustration only, the common system can include aplurality of spray levels to inject the liquid so as to contact the fluegas, which is designed to flow through such a water wash 503 at apredetermined constant velocity. The number of spray levels can bevaried depending on the effective liquid to gas (L/G) ratios. Inaddition, spray nozzles of different sizes producing different flowrates, spray patterns, and droplet sizes can also be utilized.

Step 2 (Reference Numeral 504)—The water containing the flue gas passesfrom water wash 503 to an area wherein capsules 505 are added forming aslurry 507 of water, capsules 505, CO₂, and the impurities. Carbondioxide is absorbed by passing the gas from which the carbon dioxide isto be separated through the slurry 507 either by bubbling, use of anabsorber tower, or any other means suitable for absorbing a gas into aliquid. The process for absorbing carbon dioxide or other acid gases issimilar to the process used in amine stripping.

The mixed gas is passed through or over a solution of the watercontaining the capsules 505. The water is any water which is desired tobe purified during the desorption step. This can be seawater, brine,water compromised by any low-volatility salt or other dissolvedcomponent. The water can also be a process fluid that is 100% recycled(not purified) during the desorption stage, but this is less thanoptimal. The CO₂ or other acid gases dissolve in the water and are thenabsorbed by the capsules 505, permitting more to dissolve into the wateruntil saturation is reached.

Step 3 (Reference Numerals 508, 509, 510, & 511)—The mixture of capsulescontaining the CO₂ is then heated 509 to the boiling point of water(typically 100.degree. C.) to release the CO₂ from the capsules 505.During the heating 509 step steam 511 is produced. In order to desorbthe carbon dioxide much lower temperatures are required than if the sameamines are used free in solution. Carbon dioxide is freely evolved atslightly below 100 degree C. in pure water. This is because there isrelatively little carbon dioxide gas in the water (it's partial pressure(fugacity) is lower).

Step 4 (Reference Numerals 512 & 513)—The steam 511 is condensed bycooling 513.

Step 5 (Reference Numerals 514 & 515)—Condensing of the steam 511produces fresh water 515. With a buffer media that is easily separable(by filtration) from the working liquid medium, it is now possible touse a brine or other compromised water as the feedstock. During theregeneration step the steam which must necessarily be produced can becondensed as fresh water obtaining dual benefit for the energy requiredto regenerate the CO₂. None of the buffer material carries over into thedistillate unlike the fairly volatile amines currently used. Mostimportantly, as the undesirable components of the process water (forinstance salt) build up in the bottom of the distilling process, theymay periodically be removed and the buffer material easily filtered outfrom the rejected components for return to the process. This cannot bedone easily with any of the dissolved buffer materials currently in use.One advantage is longer buffer life by reduced temperatures andisolation of the buffer material from oxygen.

Step 6 (Reference Numerals 518 & 519)—Condensing of the steam 511purifies the gas stream coming out of the process to nearly pure CO₂517. The CO₂ 517 can be used or sequestered. The CO₂ 517 can betransported to an injection site for sequestration and long-term storagein any of a variety of suitable geologic formations.

Step 7 (Reference Numerals 516 & 517)—Condensing of the steam 511 withremoval of the CO₂ 517 and water 515 leaves water with impurities 519.

Step 8 (Reference Numeral 520)—The water with impurities 519 istransferred to the water wash 103 as illustrated by the arrow 520.

Example 4

In example 4, another system for separating carbon dioxide from gasmixtures including carbon dioxide is illustrated. Example 4 isillustrated in FIGS. 6A and 6B. FIG. 6A illustrates a microcapsule CO₂machine for separating carbon dioxide from a gas mixture that includescarbon dioxide. This machine is designated generally by the referencenumeral 600 a. The microcapsule CO₂ machine 600 a is composed of thefollowing items. There is an incoming gas stream 602 that contains CO₂.There are both an inner plenum 604 and two outer plenums 606. Themicrocapsule stream 608 enters the diverter 624 and proceeds to thefirst microcapsule chamber 610 and second microcapsule chamber 612. Bothof these chambers have an inner wall 614 and an outer wall 616. Theouter plenums have exits 618. At the bottom of the chambers 610 and 612are located screw conveyors 620 and 622.

In operation a stream of microcapsules (previously described in thisapplication) enters the diverter 624 where the capsules are directedinto the two chambers 610 and 612. The capsules in these two chambersform a bed of CO₂ capturing capsules. The incoming gas stream 602 (fluegas) that contains the CO₂ the is to be captured by the microcapsulesenters the inner plenum 604 where the gas passes through inner wall 614through multiple openings that are sized to prevent the passage of themicrocapsules. The gas stream then flows through the bed of capsuleswhere the CO₂ is captured by the capsules. The gas steam then exits thecapsule bed thru outer wall 616 that also has openings sized to preventthe passage of the microcapsules. The gas stream now stripped of the CO₂now enters the outer plenums 606 where it is collected. The steam exitsthe plenums at 618 for release to the atmosphere or for furtherprocessing.

The capsules bed descends in the two chambers 610 and 612 at some ratedetermined by the capture of the CO₂ (saturation). The screw conveyorsthen transport the CO₂ saturated microcapsules to the next machine themicrocapsule regeneration machine 600 b which will be illustrated anddescribed in FIG. 6B

FIG. 6B shows the microcapsule regeneration machine 600 b. This machineis made up of many of the same items as the previous machine so we willnot list all those items but proceed to the operation of the machine.The gas stream 626 will be steam and enters the inner plenum 628. Fromthe plenum the steam passes thru the inner wall 638 that has multipleopenings again sized to prevent the passage of the microcapsules. Thesteam flows thru the bed of this time CO₂ saturated capsules and theaction of the steam will liberated the CO₂ from the capsules. The steamand the liberated CO₂ then exits the capsule bed thru the outer wall 640and be collected in the outer plenums 630. The steam and CO₂ exits theplenums 630 at openings 642 for further processing.

Various additions may be made to the basic system in order to enhancefunctionality. FIG. 8 shows a cross section of a microcapsule. In FIG.8, 801 is a layer of catalyst or enzyme added to enhance the reactionrate of carbon dioxide to dissolved carbonate. This may be eitherdissolved in the polymer, the solvent, or as a separate layer (a tripleemulsion) during bead creation. In FIG. 8, 802 shows the addition offibers, nanotubes, or other permeability-enhancing components thatimprove the permeability of the capsule, or its strength or abrasionresistance. These could include carbon nanotubes, silicon carbide,nylon, or a variety of other materials that enhance the basic functionof the polymer shell. In the case of 803 the fibers are oriented alongthe shell radius for purposes of strength improvement or abrasionresistance.

Example 5

In example 5, a system for carbon dioxide removal from gas mixtures isdescribed and illustrated. Example 5 is illustrated by FIG. 9 showing amethod of separating CO₂. The method is designated generally by thereference numeral 900. The steps of the method 900 are described below.

Method Steps—FIG. 9

Step 1 (Reference Numeral 900)—Flue gas (e.g., CO₂, H₂O, N₂, SO_(x),NO_(x)) and/or other gas mixtures is processed by passing it upwardsthrough a absorption tower while being contacted with a suspension ofpolymer coated capsules. The capsules will have a diameter and densitysuch that they are sufficiently buoyant in the upward flowing gas streamthat they behave as a fluidized bed. The system is operated such that asuitable contact time is achieved for gas reactions to take place andCO₂ separated from the gas mixture. During contact with the gas mixture,the capsules will over time become enriched in CO₂ because the solventcontained within the capsule has a strong affinity for CO₂. Some or mostof the CO₂ originally in the gas mixture is now contained within thecapsules.

The solvent may be an amine, an inorganic base, or any other solventwhich has a high capacity for take-up of CO₂. Preferential partitioningof CO₂ into the capsule is due to the relatively higher solubility ofCO₂ in the encapsulated solvent vs. other components of the mixed gasstream such as nitrogen or oxygen. The capsules remain in the gas streamuntil they contain sufficient CO₂ such that they are ready for removalfrom the gas contactor for transport to the regenerator where thecontained CO₂ will be removed.

In one embodiment, the capsules remain in the system for some period oftime before they are entirely removed from the system. As such thesystem is operated in a batch mode.

In another embodiment, the capsules are fed and removed continuously ata rate such that the mean residence time allows for sufficient CO₂recovery to meet requirements. In this case, not all the capsules willbe fully loaded but the average loading is sufficient to provide for thedesired flux of CO₂ removal. As such the system operates in a continuousmode.

In another embodiment, the capsule solvent is chosen and designed suchthat as the capsules load with CO₂ they become progressively more densethan unloaded capsules and as a consequence the loaded capsulesself-separate and drop to the bottom of the tower where they are removedfor transport to the regenerator described in Step 2. As such the systemoperates in a continuous mode.

In another embodiment, the capsules contact the mixed gas stream in arotating tipped cylinder such that the capsules form a bed residing onthe lower surface of the rotating cylinder and cascade down the lengthof the cylinder, while the gas stream passes upwards through thecylinder contacting the cascading capsules. At the bottom, the capsulesare removed and cycled back to the top for additional loading. In thisembodiment, the system may be operated either in batch or continuousmode. The advantage for this contact method is that the capsules nolonger must be sufficiently buoyant such that they form a fluidized bedin the gas tower, as is the case for the other contact scenarios.

The solvent contained within the capsule is chosen such that is has apreferentially high solubility of CO₂ and low solubility of other gasstream components such as nitrogen and oxygen. Solvents that arealkaline have this property because the CO₂ will ionize in them to formbicarbonate (HCO₃—) and carbonate (CO₃—) species which are highlysoluble in aqueous solutions and in aqueous solutions of amines. Thesolvent of choice may be an amine such as methylethanolamine (MEA) orother amine-based solvents that have high solubilities for CO₂. Thesolvent may be an inorganic solution of a base, such as sodiumhydroxide, potassium carbonate, sodium borate, or sodium phosphate orany of many other inorganic solvents that are bases in the sense ofacid-base reactions, and have high solubilities of carbon dioxide. It isthe solvent that provides selectivity for CO₂. The capsule wall will bepermeable to all of the gas components including water, and does notprovide selectivity for CO2.

Step 2 (Reference Numeral 900)—The loaded “fat” capsules from Step 1 arenow ready for CO₂ extraction “regeneration” in order to produce aconcentrated CO₂ stream. The goal is to produce a relatively pure streamof CO₂ such that it can be compressed to a liquid form for transport orstorage. As such the derived CO₂ stream must not contain appreciableamounts of non-condensable gases such as nitrogen, oxygen or argon.

Regeneration to remove the contained CO₂ is carried out by heating thecapsules to an elevated temperature where the equilibrium content of CO₂is much lower than the equilibrium content of CO₂ during collection fromthe mixed gas stream. The temperature may be around 100 C or may be amuch higher temperature. The optimal temperature of regeneration dependson the type of solvent contained within the capsule and the CO₂ loading.

The capsules may be regenerated by contacting them with hot steam, whichwill produce a gas containing mainly CO₂ and H₂O, and which upon coolingwill self-separate into a dominantly CO₂ gas phases and liquid water(Step 3).

The capsules may be regenerated by heating in pressurized liquid waterwhich will upon lowering of the containing pressure will produce astream of relatively pure CO₂.

During heating, CO₂ and water escape from the capsule into thesurrounding gas phase. The solvent is chosen such that it is notvolatile at the temperature of regeneration and therefore does notpreferentially leave the capsule with CO₂ and water, although smallamounts may leave the capsule for some solvents and can be tolerated forsome applications. In addition, for sparingly volatile solvents such asamines, the capsule shell reduces the flux of the solvent out of thecapsule. This allows the working temperature of regeneration for theencapsulated solvent to be higher than is possible for systems where theamine solvent is not encapsulated. Regeneration at a higher relativetemperature produces a higher partial pressure of CO₂ which lowers theenergy needed for compression and liquification of CO₂ which may lowersthe overall cost of CO₂ collection.

Another advantage of encapsulation of amine solvents is that the liquidamine does not directly contact materials used in the regenerator, suchas metals, which reduces corrosion and allows potentially less expensiveconstruction materials. For example, carbon steel can be used to replacestainless steel. A related benefit is that if thermal degradation of thesolvent takes place, the degradation products tend to remain within thecapsules and do not contact the containment housing and in so doingcause damage due to corrosion or scaling.

Step 3 (Reference Numeral 900)—The regenerated capsules that have beenthermally treated are now have low CO₂ contents (“lean”) and aresuitable for another cycle of CO₂ capture. The capsules may be removedfrom the gas or liquid water using a mechanical filter of any of avariety of type and designs. The separated capsules are then returned toStep 1 to begin another cycle.

Separation of the CO₂ from water takes place by cooling the hot gas toproduce liquid water and a separate CO₂ gas phase. It is advantageous inthis step and in the overall process to make use of heat exchangers tocapture heat from the condensation of steam, if it is generated, and useit to heat the incoming “fat” stream of encapsulated CO₂.

The carbon dioxide that has been separated from the gas mixture can besold, stored, sequestered, or otherwise disposed of.

Example 6

In example 6, a system for nitrous oxide removal from gas mixtures isdescribed. Capsules having a polymer coating and stripping solventsencapsulated in the capsules are provided. The polymer coating ispermeable to nitrous oxide. The polymer coated capsules are exposed tothe gas mixture that includes nitrous oxide. The nitrous oxide migratesthrough the polymer coating of the capsules and is taken up by thestripping solvents. The nitrous oxide is separated from the gas mixtureby driving off the nitrous oxide from the polymer coated capsules. Thismay be accomplished, for instance, by heating the polymer coatedcapsules. For example, steam can be directed onto the polymer coatedcapsules to drive off the nitrous oxide from the capsules. The nitrousoxide that has been separated from the gas mixture can be disposed of.

Example 7

In example 7, a system for hydrogen sulfide removal from gas mixtures isdescribed. Capsules having a polymer coating and stripping solventsencapsulated in the capsules are provided. The polymer coating ispermeable to hydrogen sulfide. The polymer coated capsules are exposedto the gas mixture that includes hydrogen sulfide. The hydrogen sulfidemigrates through the polymer coating of the capsules and is taken up bythe stripping solvents. The hydrogen sulfide is separated from the gasmixture by driving off the hydrogen sulfide from the polymer coatedcapsules. This may be accomplished, for instance, by heating the polymercoated capsules. For example, steam can be directed onto the polymercoated capsules to drive off the hydrogen sulfide from the capsules. Thehydrogen sulfide that has been separated from the gas mixture can bedisposed of.

Example 8

In example 8, a system for sulphates removal from gas mixtures isdescribed. Capsules having a polymer coating and stripping solventsencapsulated in the capsules are provided. The polymer coating ispermeable to sulphates. The polymer coated capsules are exposed to thegas mixture that includes sulphates. The sulphates migrates through thepolymer coating of the capsules and is taken up by the strippingsolvents. The sulphates is separated from the gas mixture by driving offthe sulphates from the polymer coated capsules. This may beaccomplished, for instance, by heating the polymer coated capsules. Forexample, steam can be directed onto the polymer coated capsules to driveoff the sulphates from the capsules. The sulphates that has beenseparated from the gas mixture can be disposed of.

Capsule Making System

FIG. 7 illustrates a system for making polymer coated capsules. FIG. 7illustrates a system and method of fabricating double-emulsionmicrocapsules. The schematically illustrated method 700 will be composedof the following items. The injection tube 702 with a ID (um) and OD1000 (um), a collection tube 704 with an ID of 500 (um) and OD 1000 (um)and an outer tube 706 of square cross section with ID of 1000 (um) andID of 1200 (um).

In operation the inner fluid 708 (MEA/H2O) with a viscosity of 10-50(cP) and a flow rate of 200-800 (Ulh-1) flows in the injection tube 702in the direction indicated by arrow 710. As this fluid proceeds itpasses thru a droplet forming nozzle 712. The formed droplet is releasedfrom the nozzle and becomes encased in the middle fluid 714 (NOAPre-polymer) with a viscosity of 10-50 (cP) and flow rate of 200-800(uLh-1), the middle fluid 714 is flowing in the direction indicated byarrow 716. The inner fluid droplet 708 becomes encased in the middlefluid 714 forming an encapsulated microcapsules 718 that have a CO2capturing solvent core with a thin CO₂ permeable outer shell. The outerfluid (PVA Stabilizer) with a viscosity of 10-50 (cP) and a flow rate of200-800 (uLh-1) flowing in the outer tube 706 in the direction indicatedby arrow 722. This outer fluid 720 carries the fabricated microcapsules718 into the collection tube 704. There is a boundary layer 724 thatprevents the middle fluid 714 and outer fluid 720 from mixing as theyhave a large difference in both their viscosity and flow rates. Theabove described method will produce Microcapsules of a controlled sizewith an inner fluid (solvent/catalyst) enclosed in a CO₂ permeablepolymer shell.

Systems for producing microcapsules are described in U.S. Pat. No.7,776,927 and in U.S. Published Patent Application Nos. 2009/0012187 and2009/0131543. U.S. Pat. No. 7,776,927 to Liang-Yin Chu et al, assignedto the President and Fellows of Harvard College, discloses emulsions andthe production of emulsions, including multiple emulsions andmicrofluidic systems for producing multiple emulsions. A multipleemulsion generally describes larger droplets that contain one or moresmaller droplets therein which, in some cases, can contain even smallerdroplets therein, etc. Emulsions, including multiple emulsions, can beformed in certain embodiments with generally precise repeatability, andcan be tailored to include any number of inner droplets, in any desirednesting arrangement, within a single outer droplet. In addition, in someaspects of the invention, one or more droplets may be controllablyreleased from a surrounding droplet. U.S. Published Patent ApplicationNo. 2009/0012187 to Liang-Yin Chu et al, assigned to the President andFellows of Harvard College, discloses multiple emulsions, and to methodsand apparatuses for making emulsions, and techniques for using the same.A multiple emulsion generally describes larger droplets that contain oneor more smaller droplets therein which, in some cases, can contain evensmaller droplets therein, etc. Emulsions, including multiple emulsions,can be formed in certain embodiments with generally preciserepeatability, and can be tailored to include any number of innerdroplets, in any desired nesting arrangement, within a single outerdroplet. In addition, in some aspects of the invention, one or moredroplets may be controllably released from a surrounding droplet. U.S.Published Patent Application No. 2009/0131543 to David A. Weitzdiscloses multiple emulsions, and to methods and apparatuses for makingmultiple emulsions. A multiple emulsion, as used herein, describeslarger droplets that contain one or more smaller droplets therein. Thelarger droplet or droplets may be suspended in a third fluid in somecases. In certain embodiments, emulsion degrees of nesting within themultiple emulsion are possible. For example, an emulsion may containdroplets containing smaller droplets therein, where at least some of thesmaller droplets contain even smaller droplets therein, etc. Multipleemulsions can be useful for encapsulating species such as pharmaceuticalagents, cells, chemicals, or the like. In some cases, one or more of thedroplets (e.g., an inner droplet and/or an outer droplet) can changeform, for instance, to become solidified to form a microcapsule, a liposome, a polymero some, or a colloidosome. As described below, multipleemulsions can be formed in one step in certain embodiments, withgenerally precise repeatability, and can be tailored to include one,two, three, or more inner droplets within a single outer droplet (whichdroplets may all be nested in some cases). As used herein, the term“fluid” generally means a material in a liquid or gaseous state. Fluids,however, may also contain solids, such as suspended or colloidalparticles. U.S. Pat. No. 7,776,927 and U.S. Published Patent ApplicationNos. 2009/0012187 and 2009/0131543 are incorporated herein by thisreference.

Mass Transfer

Encapsulated solvents can be used to capture carbon dioxide from powerplant flue gas. The limiting step in mass transfer is probably diffusionacross the polymer membrane. The mass transfer rate is then proportionalto the permeability of the membrane. Permeability has a wide range ofvalues for different polymers. A permeability for CO₂ of 100 barrer ischosen as a benchmark because it is higher than most polymers but can beachieved with several different chemistries. At 100 barrer permeability,200 μm diameter, and 5 μm wall thickness, encapsulated solvents haveabout 2 orders of magnitude slower absorption per unit surface area thanconventional liquid solvents.

A bed of spherical beads is explored as a system design. With 200 μmdiameter beads and close spherical packing, such a bed has 2 orders ofmagnitude higher surface area per unit absorber volume than aconventional packed tower using a liquid solvent. High pressure dropappears to be the primary drawback of this configuration, which isestimated to be orders of magnitude larger than for a conventionalpacked tower. The high pressure drop is largely due to the lowproportion of void space in tight-packed spheres (36%-40%, compared with90-97% in commercial tower packings).

A system based on a packed bed of beads will be viable if a higherpermeability can be achieved (on the order of 1000 barrer), or if morevoid space can be introduced to the system (e.g. a doubling). Inprinciple, resistance to mass transfer of CO₂ into (or out of) the beadcan occur in three zones: (1) from the bulkgas to the surface of thepolymer shell (gas-phase resistance), (2) through the polymer shell(membrane resistance), and (3) from the inner surface of the shell tothe bulk of the inner fluid (liquid-phase resistance). For thiscalculation, Applicants assume that membrane resistance isoverwhelmingly the slowest step and therefore controls mass transfer. Inthis case the flux across the membrane, J, is given by:

$\begin{matrix}{J = {\frac{{mass}\mspace{14mu} {transfer}\mspace{14mu} {rate}}{{surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {membrance}} = {\frac{P\; \Delta \; p}{L}\left\lbrack \frac{mol}{m^{2}s} \right\rbrack}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where Δp is the pressure drop across the membrane, L is the thickness ofthe membrane, and P is the permeability coefficient of the polymer. Forour purposes, the CO₂ pressure on the outside of the shell is thegas-phase partial pressure in the flue gas. Since Applicants assume theinner fluid is a fast solvent, the effective CO₂ pressure on the innerwall of the shell is the equilibrium partial pressure of CO₂ above thesolvent at the appropriate temperature and carbon loading. This isgenerally small compared to the partial pressure in the flue gas. Forexample, flue gas typically starts at 15% CO₂=0.15 atm=15200 Pa. Theequilibrium partial pressure of CO₂ for 5M Monoethanolamine (MEA) at 40°C. and 0.3 mol CO₂/mol amine is 22 Pa. So for our purposes, Δp is equalto the partial pressure of CO₂ in the flue gas.

The permeability coefficient depends slightly on temperature andpressure, but is mostly a function of the polymer(s) comprising themembrane. It ranges at least four orders of magnitude. The literature ongas separation with membranes makes much of the trade-off betweenpermeability and “selectivity”, that is, the relative permeabilities ofCO₂ and N₂. Higher permeabilities are usually achieved with lowerselectivity, and vice versa. However, Applicants achieve selectivitythrough the solvent, which reacts with CO₂ and not with N₂, which maydrive us toward the most permeable polymer that meets structuralrequirements. Alternatively, Applicants may be limited by relativeselectivity of the membrane for CO₂ over solvent.

The synthetic polymer with the largest measured permeabilities ispoly(1-trimethylsilylpropyne). This polymer possesses a carbon dioxidepermeability of 28,000 barrer and a nitrogen permeability of 4970barrer. These very large permeabilities are associated with a very largefractional free volume. These permeabilities tend to decrease with timedue to slow crystallization of the polymer. This effect can becounteracted by the addition of certain additives.

However, for now Applicants will set aside the possibility of a membranewith very high fractional free volume and consider the more typicalpolymers. Without knowing the constraints on polymer choice for theencapsulation, Applicants choose 100 barrer as the base casepermeability because it appears to be achievable with a variety ofdifferent chemistries (polyimides, polyacetylenes, polycarbonates).Applicants will keep in mind that this may be a conservative choice. Forperspective, Applicants can compare a permeability of 100 barrer to somerepresentative mass transfer coefficients in CO₂ capture systems.Equation 1 is analogous to the classic mass transfer equation across aninterfacial boundary:

J=KΔC

where K is the overall mass transfer coefficient and ΔC is theconcentration difference between, in our case, the bulk flue gas and theequilibrium partial pressure of CO₂ above the solvent. If Applicantscajole P and Δp into units of concentration (assuming STP), thenApplicants have P/L⇄K in units of length per time. In these units, bothcoefficients are what physicists might call the “piston velocity”. Thatis, if there were a piston above the interface, moving steadily at thepiston velocity and pushing flue gas across the boundary, you would getan equivalent mass transfer rate of CO₂. Although there are numerouscaveats in comparing these numbers (one being that P is measuredempirically using a single gas and a physical pressure drop and themembranes may respond differently to an equivalent concentrationgradient), Applicants think it is a safe conclusion that, under ourassumptions, mass transfer across the membrane is about 2 orders ofmagnitude slower than across the interface of a liquid solvent.

However, the mass transfer rate is proportional to surface area, andencapsulation has the potential to provide a lot of surface areacompared to standard liquid-gas system. Consider a bed ofrandomly-packed spherical beads of equal diameter, d and packing density_ (volume of beads/bulk volume). The surface area per bulk volume ofabsorber is:

$\begin{matrix}{\frac{S}{V} = {\frac{\pi \; d^{2}}{\frac{1}{G}\pi \; {d^{3}/\rho}} = \frac{6\; \rho}{d}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

For close random packing of spheres, typical values of _ range from 0.60to 0.64. For comparison, packings for gas/liquid absorbers have solidsurface area in the range of 100-1000 m2/m3. The effective interfacialarea is usually less, because not all surfaces get wet and some poolsstagnate and saturate. Typical values for an MEA system would be 250m2/m3 for the packing and about 80% area utilization. Thus, Applicantshave about two orders of magnitude more surface area in a bed of packedbeads than in a typical liquid absorber. So, even with our two orders ofmagnitude slower mass transfer, the mass transfer performance of thebeads is equal to a packed tower. Higher permeabilities, as have beenobtained with semicosil, improve the performance.

As a benchmark, Applicants may consider the minimum time it takes for abead filled with MEA to reach saturation. Building from Equation 1, theloading time, τ, for a bead to reach the liquid saturation concentrationof CO₂, Csat, is given by:

$\mspace{20mu} {\tau = {\frac{\left( {{volume}\mspace{14mu} {of}\mspace{14mu} {bead}} \right) \cdot \text{?}}{\left( {{surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {bead}} \right) \cdot ({flux})} = {\frac{\frac{1}{6}\pi \; d^{3}C_{sat}}{\pi \; d^{2}P\; \Delta \; {p/L}} = \frac{\text{?}{Ld}}{6\; P\; \Delta \; p}}}}$?indicates text missing or illegible when filed

The theoretical Csat for MEA is 0.5 mol CO₂/mol MEA, which for a 30 wt %MEA solution comes to about 10 wt % CO₂ or 2.4 M. as a function of beaddiameter and wall thickness. This appears to be due to differentassumptions about permeability.

Two important parameters for a capture system are gas flow rate andabsorber height. The two together determine the capture effectivenessfrom flue gas

=(1−CO₂ out/CO₂ in). And while slowing the gas low rate increaseseffectiveness (by increasing the residence time of the gas), it alsodecreases capital utilization. For example, at half the gas flow rateone needs twice as many absorber towers (or one tower with twice thecross-section) for the same throughput. Absorber height and gas flowrate both also determine the pressure drop across the absorber which inturn contributes to energy use. Thus, a meaningful selection of gas flowrate and absorber height cannot be made without considering capital costagainst the cost of energy. However, Applicants can make some roughassumptions to see if Applicants are in a tenable design space.

Suppose again that Applicants have a bed of randomly-packed beads ofdiameter d and packing density p. If the mass transfer rate followsEquation 1 then mass transfer is first order with the CO₂ concentrationin the flue gas. As a parcel of gas moves through the absorber, the CO₂concentration then follows first order decay:

C(t)=C _(in) e ^(−K) ^(gas) ^(t)

where C(t) is the concentration of CO₂ in the gas parcel at time t andKgas is the rate constant of CO₂ loss with units of inverse time.Applicants can also think of Kgas as the mass transfer rate in theparcel per unit concentration:

$\mspace{20mu} {K_{gas} = {\frac{Q}{V_{gas}} \cdot \frac{1}{C\left( \text{?} \right)}}}$?indicates text missing or illegible when filed

Combining Equations 1 and 2 Applicants have the mass transfer rate perunit volume of absorber:

And the volume of gas per unit volume absorber is:

$\begin{matrix}{\mspace{79mu} {{\frac{V_{gas}}{V} = \left( {1 - \text{?}} \right)}{\text{?}\text{indicates text missing or illegible when filed}}}} & \;\end{matrix}$

Applicants are almost ready to combine the above three equations to findKgas but Applicants have a slight snag in that P is defined to includeunits of inverse pressure instead of inverse concentration. As in Table1, Applicants will cajole P to include units of inverse concentration byassuming STP. Applicants can then replace Δp by C and get:

$\mspace{20mu} {K_{gas} = {{\frac{Q}{V_{gas}} \cdot \frac{1}{C(t)}} = {{\frac{6\; {{PC}\left( \text{?} \right)}\text{?}}{{{dL}\left( {1 - \text{?}} \right)}V} \cdot \frac{1}{C\left( \text{?} \right)}} = \frac{6\; {Pp}}{{dL}\left( {1 - \text{?}} \right)}}}}$?indicates text missing or illegible when filed

Applicants can now calculate the residence time of flue gas, τgas,required for a particular capture effectiveness,

For CO₂ capture from power plants, Applicants typically assume thecapture system must be at least 90% effective. For our base case ofP=100 barrer, wall thickness=5 μm, and d=100 μm, Applicants calculate aresidence time of 1.6 s. Again, the flow rate of gas in the tower is atunable parameter, but for a sense of scale Applicants can consider thatthe superficial velocity in a large-scale packed tower is typically onthe order of 1 m/s. That would put the absorber height in our base caseat about 4 m. This is comfortably inside the realm of industrialpractice for a packed tower. However, the types of packings used inthose towers have much more void space—90-97% in the physical packing,compared with our 38%.

The pressure drop across a bed of packed spheres is a well-studiedproblem. It can be estimated from the semiempirical Ergun Equation,which derives from an energy balance on kinetic energy and frictionallosses:

$\begin{matrix}{\mspace{79mu} {{\frac{\Delta \text{?}}{H} = {{150 \cdot \frac{\text{?}\mu \; \text{?}}{{\Phi^{2}\left( {1 - \text{?}} \right)}^{3}d^{2}}} + {1.75 \cdot \frac{{\text{?} \cdot \text{?}}\text{?}}{\left( {1 - \text{?}} \right)^{3}\Phi \; d}}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & \;\end{matrix}$

where:

ΔP is the pressure drop across the bed [Pa]

H is the height of the bed [m]

p is still the bulk packing density of beads, assumed 0.62

μ is the dynamic viscosity of the fluid, assumed 2.0×10-5 kg/(m·s) (thedynamic viscosity of air at 40° C.)

In the previous sections on packed towers, Applicants found that thetower height required for a given capture effectiveness is proportionalto the superficial gas velocity, Vs:

$\mspace{20mu} {H = \frac{\text{?} \cdot \tau_{gas}}{\left( {1 - \text{?}} \right)}}$?indicates text missing or illegible when filed

However, the cross-sectional area of the tower required for a given flowof flue gas is inversely proportional to the velocity:

$\mspace{20mu} {{Area} = \frac{Flowrate}{\text{?}}}$?indicates text missing or illegible when filed

which means that the packing volume (H×Area) is actually constant withVs. Applicants also know that the pressure drop falls strongly with Vs.Therefore, if one had a very wide, very short tower, one may be able toovercome the pressure drop concerns of a conventional packed towerwithout necessarily needing more beads. In a conventional configuration,this would be impractical, because space and capital required for flowdistributors would be overwhelming and edge effects would diminish masstransfer efficiency. But perhaps these problems can be overcome byturning the tower on its side, if you will.

Grain drying systems, which contact massive amounts of granular solidswith hot air, offer a good analogy for encapsulated solvents. There aremany types of systems for grain and similar drying applications,including fluidized beds, rotating trays, and many which look much likea typical packed bed. A type of continuous flow drying system, as shownin FIGS. 6A and 6B, can be use. In this type of system, solids are heldbetween vertical and slanted perforated walls while gas is blownperpendicular to the walls. Wet solids are added to the top of the wallswhile dry solids are removed slowly from the bottom by paddle-wheel type“metering rolls”. The advantages of this configuration are (1) the largeeffective cross-sectional area achieved by flowing the gas horizontallyand stacking the solids vertically, (2) the low gas velocity required inturn, and (3) the independent rate of solids circulation, allowingcontinuous flow operation. Differences between grain drying and carboncapture with encapsulated amines include particle sizes (grains tend tobe mm scale or larger), particle strength and flow characteristics, andpotentially different regimes of residence time and pressure drop. Inparticular, the walls of the absorber must contain much smallerparticles and probably withstand a higher pressure drop than the wallsof an analogous grain dryer.

Applicants can model the walls of moving-bed system as a perforatedplate through which the flue gas must flow. The holes should allow gasto pass through but retain the beads without impeding their movement.Applicants assume the plate is made from solid steel or similar alloy,as opposed to a wire mesh or fabric. These latter options would yield alower pressure drop and probably lower capital expense, but could nothold against much total pressure and might abrade the beads. Theconclusion of this section is that the pressure drop across anappropriate plate is generally less than 1 kPa-small compared to thelikely pressure drop across the beads themselves. However, the strengthof the plates, and the ease of fabricating relatively small holes inthick plates, may be nontrivial considerations.

Empirical correlations for pressure drop across a perforated plate whichdepend only on open area and air velocity are widely available. However,these are based on plates with much larger holes than Applicantsrequire, which allows the friction of flow inside the hole, and thus thethickness of the plate, to be neglected.

In general, the pressure drop across a perforated plate, ΔP_(plate)consists of losses from compression of the gas into the holes, frictionthrough the holes, and then expansion on the other side. The followingexpression can be used for calculating the pressure drop across a dry,perforated plate. The terms within the brackets address those threekinds of losses, respectively:

$\mspace{20mu} {\text{?} = {{k\left\lbrack {{0.4\left( {1.25 - \frac{A_{h}}{A_{c}}} \right)} + {4\; {f\left( {T/d_{h}} \right)}} + \left( {1 - \frac{A_{h}}{A_{c}}} \right)^{2}} \right\rbrack}\frac{V_{h}^{2}\text{?}}{2}}}$  where:$\mspace{20mu} {\text{?}\frac{A_{h}}{A_{c}}\mspace{14mu} {is}\mspace{14mu} {the}\mspace{14mu} {ratio}\mspace{14mu} {of}\mspace{14mu} {hole}\mspace{14mu} {area}\mspace{14mu} {to}\mspace{14mu} {total}\mspace{14mu} {plate}\mspace{14mu} {area}\text{?}}$  ?T  is  the  thickness  of  the  plate[m]  ?d_(h)  is  the  diameter  of  the  holes [m]${\text{?}V_{h}\mspace{14mu} {is}\mspace{14mu} {the}\mspace{14mu} {velocity}\mspace{14mu} {of}\mspace{14mu} {gas}\mspace{14mu} {inside}\mspace{14mu} {the}\mspace{14mu} {{hole}\mspace{14mu}\left\lbrack {m\text{/}s} \right\rbrack}},\; {{{which}\mspace{14mu} {is}\mspace{14mu} {related}\mspace{14mu} {to}\mspace{14mu} {the}\mspace{14mu} {superficial}\mspace{14mu} {velocity}\mspace{14mu} {by}\text{:}\mspace{14mu} V_{h}} = \frac{\text{?}}{\text{?}}}$  ??  is  the  ?  friction  factor, discussed  below??k  is  an  empirical  correction, given  by  ???  as  a  complicated  function  of  T/d_(k).  It  ranges  from  about  0.85  to  1.9??indicates text missing or illegible when filed

The Fanning friction factor (equal to one fourth of the Darcy frictionfactor) is a function of the Reynolds number of the system, Re, whichfor flow through smooth, circular pipes, and correcting the superficialvelocity to the velocity inside the holes, is defined by:

$\mspace{20mu} {\text{?} = \frac{\text{?}V_{s}d_{h}}{\mu \left( {A_{h}/A_{c}} \right)}}$?indicates text missing or illegible when filed

In our reasonable parameter space, Re ranges from 0.32 to 32, which issolidly in the laminar flow regime (for flow in a pipe, Re<2300 isgenerally laminar). In the laminar regime, Applicants can calculate theFanning friction factor by:

$\mspace{20mu} {\text{?} = \frac{16}{\text{?}}}$?indicates text missing or illegible when filed

Now Applicants have to make some assumptions about the hole size andthickness of the plates. It seems fairly obvious that the holes shouldbe smaller than the beads (dh<d), but not much smaller. Applicants willassume dh=75 μm for the base case. The required thickness of the plateis a structural engineering question that can't really be answeredwithout a detailed system design. However, the wall thickness of steelpressure vessels may offer some guidance. From the previous discussionon packed beds, Applicants may expect pressure drops across the bed onthe order of 100 kPa. For a large (diameter=2 m), cylindrical vessel oftypical steel at that pressure, the required wall thickness is 1.2 mm.One can play with the assumptions about curvature, pressure, and steelstrength and get +/− a factor of 3 or so. Now, for our hole size, 1.2 mmactually gives a T/dh ratio a factor of 2 outside the range ofMcAllister et al.'s data, and thus Applicants don't know quite what touse for k (assume k=2) because at the end of the range, k=1.5 and istrending up. It also may be challenging from a fabrication perspective.Applicants haven't seen many applications using holes that small, letalone with such thick plates. On the other hand, the structural designspace is so open that thicker plates should be usable.

The last parameter to consider is the fraction of open area, Ah/Ac.Perforated metals are commonly available with open area up 60% (IPA,1993), however, that comes at the price of reduced strength. At 20% openarea, strength is reduced by about 50%; at 60% open area, strength isreduced to 15-20% of solid-plate strength. Applicants have assumed 20%open area.

The most important thing to note from these results is probably that they-axis is in Pa instead of kPa; these pressure drops are small comparedto the pressure drop across a bed of beads.

Applicants will assume a capture effectiveness of CO₂ from flue gas of90%. With the height fixed, the gas velocity, Vs, is adjusted to achieve90% capture. The pressure drop can then be calculated. Much of thisparameter space seems to fall under the rough upper bound Applicantsproposed for pressure drop of 140 kPa, which is encouraging. Aninteresting feature of the moving-bed configuration is that the pressuredrop is higher for higher-permeability beads, because the gas is beingpushed though faster. The trade-off is capital cost: the higher thepermeability, the less wall area is required for a given size powerplant.

Now let's put the pieces together in an example. Suppose Applicants have200 μm beads with 400 barrer permeability. The superficial velocityrequired to achieve 90% capture is 0.18 m/s. At this rate, Applicantsneed 49 commercial grain dryer-sized units to handle a 430 MWe coalplant. Each operates with a pressure drop of 34.7 kPa across the bed and0.25 kPa across the inner and outer walls (assuming 1.2 mm wallthickness). In energy terms, Applicants expect that this pressure dropis entirely manageable. Notably, the force due to the pressure drop mustbe resisted physically by the outer wall and by the beads, especiallythose closest to the outer wall, 35 kN/m2 is a substantial force,equivalent to being at the bottom of about 12 ft of water column. Theleft side of the beads on the left side of the diagram are being pressedagainst the outer wall with that force, which translates to about 2 mNper bead. Nanoidentor compression tests are analogous to this situation.Applicants have not conclusively tested our own beads yet, but estimatesbased on the literature and polymer properties indicate that they willbe able to withstand tens of mN of force before rupturing. Supposingthis is correct and the beads are not at risk of rupturing, they stillmay substantially deform, which in turn would decrease void space andincrease pressure drop. And so investigation of the deformationproperties of the beads appears to be in order. Another concern is thatthe pressure would pin the beads in place, impeding flow which in graindrying systems occurs by gravity. The leftward pressure on the leftmostbeads overwhelms gravity by a factor of 4×105 which seems to precludeany gravitational settling of the beads. Applicants could overcome thisby giving the gas flow a downward component, for example by having moreholes toward the bottom of the outer wall.

Catalysis and Choice of Working Solvent

The working model is that CO₂ physically diffuses through the polymershell and then reacts in the inner fluid to form carbonates orcomplexes. This approach implies that a catalyst, if used, should bedissolved in the inner fluid or anchored to the inner surface of theshell. The catalyst is only helpful in this case if reaction in thesolvent would otherwise slow mass transfer. In the previous calculationsApplicants assumed that reaction in the solvent did not significantlyslow the reaction, either by use of a fast solvent or by enhancing thereaction with a catalyst.

Mass transfer through a series of media can be described by theelectrical resistance model, where the resistance, R, is the inverse ofthe mass transfer coefficient, K. If Applicants neglect gas-sideresistance (which is probably a good assumption), then Applicants have:

$\mspace{20mu} {\begin{matrix}{R_{total} = {\text{?} + \text{?}}} \\{\frac{1}{K_{total}} = {\frac{1}{\text{?}} + \frac{1}{\text{?}}}}\end{matrix}}$ ?indicates text missing or illegible when filed

If one mass transfer coefficient is much smaller than the other, it willtend to dominate the total and the larger one can be neglected. In abead filled with one of these solvents, the “equivalent permeability” isthe permeability for which the shell and solvent are contributingequally to mass transfer resistance. For example, for a bead with 5/mwall thickness filled with 0.33 M NaOH, the equivalent shellpermeability is 10,000 barrer. If Applicants had a shell with 1,000barrer permeability, then the solvent would be contributing only 9% ofthe total resistance, which is to say, addition of a catalyst couldspeed the rate of mass transfer by, at most, 9%. If Applicants had ashell with permeability of 10,000, then a catalyst could speed the rateof mass transfer by, at most, 50%.

Note that K depends on a number of factors, such as turbulence in themeasurement system, temperature, and precise composition of thesolution, so these values should be taken as order-of-magnitude guidesonly. However, considering that the highest measured permeability for apolymer membrane is 28,000 barrer, it seems apparent that a catalystwould not be very helpful in beads filled with a fast-reacting solventlike MEA. However, the catalyst should be helpful for a slower solventlike sodium bicarbonate, paired with a membrane with permeability of afew hundred barrer or higher.

Those conclusions still assume that the catalyst is dissolved in theinner fluid or anchored to the inner surface of the shell. Analternative approach would be to embed catalyst in the polymer shell oron the outer surface of the shell. This approach implies that CO₂ ishydrolyzed on the outer surface or somewhere inside the shell materialand then diffuses to the inner fluid as carbonate. In this case,Applicants can model the shell as an immobilized liquid membrane. Theshell material has micro- or nano-pores where the solvent is held bycapillary pressure. CO₂ diffuses from the outside of the capsule to thebulk fluid on the inside through the pore liquid. Mass transfer into thebeads is controlled by diffusion and reaction of species in the porechannel, including CO₂ (aq), HCO⁻ ₃, and protonated and unprotonatedbuffer. The catalyst must be present in the pore channel to beeffective.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. An apparatus for separating a target substance from a fluid ormixture, comprising: a system for exposing capsules having a coating andstripping material encapsulated in said capsules to the fluid ormixture, wherein said coating is permeable to the target substance andwherein the target substance migrates through said coating and is takenup by said stripping material; and a system for driving off the targetsubstance from said capsules thereby separating the target substancefrom the fluid or mixture.
 2. The apparatus for separating a targetsubstance from a fluid or mixture of claim 1 wherein said strippingsolvents are primary, secondary, tertiary, and hindered amines, causticsolutions, ionic buffer solutions, ammonia, or other solvents havingsolubility of carbon dioxide.
 3. The apparatus for separating a targetsubstance from a fluid or mixture of claim 1 wherein said strippingsolvents are amines.
 4. The apparatus for separating a target substancefrom a fluid or mixture of claim 1 wherein said coating is made of aporous solid.
 5. The apparatus for separating a target substance from afluid or mixture of claim 1 wherein said coating includes carbon fibers.6. The apparatus for separating a target substance from a fluid ormixture of claim 1 wherein said coating includes nanotubes.
 7. Theapparatus for separating a target substance from a fluid or mixture ofclaim 1 wherein said coating is made of any of several families ofpolymers, including polystyrene, polyethylene, polypropylene, and nylon.8. The apparatus for separating a target substance from a fluid ormixture of claim 1 wherein the target substance is carbon dioxide andwherein said coating is permeable to carbon dioxide and wherein thecarbon dioxide migrates through said coating and is taken up by saidstripping material and wherein said system for driving off the targetsubstance from said capsules thereby separating the target substancefrom the fluid or mixture is a system for driving off carbon dioxidefrom said capsules.
 9. The apparatus for separating a target substancefrom a fluid or mixture of claim 1 wherein the target substance isnitrous oxide and wherein said coating is permeable to nitrous oxide andwherein said nitrous oxide migrates through said coating and is taken upby said stripping material and wherein said system for driving off thetarget substance from said capsules thereby separating the targetsubstance from the fluid or mixture is a system for driving off saidnitrous oxide from said capsules.
 10. The apparatus for separating atarget substance from a fluid or mixture of claim 1 wherein the targetsubstance are sulphates and wherein said coating is permeable to saidsulphates and wherein said sulphates migrate through said coating andare taken up by said stripping material and wherein said system fordriving off the target substance from said capsules thereby separatingthe target substance from the fluid or mixture is a system for drivingoff said sulphates from said capsules.
 11. The apparatus for separatinga target substance from a fluid or mixture of claim 1 wherein the targetsubstance is hydrogen sulfide and wherein said coating is permeable tosaid hydrogen sulfide and wherein said hydrogen sulfide migrates throughsaid coating and is taken up by said stripping material and wherein saidsystem for driving off the target substance from said capsules therebyseparating the target substance from the fluid or mixture is a systemfor driving off said hydrogen sulfide from said capsules.
 12. A capsulefor separating a target substance from a fluid or mixture, comprising: acapsule body, a surface layer on said capsule body that is permeable tothe target substance, and stripping solvents encapsulated within saidcapsule body, wherein said stripping solvents are soluble to the targetsubstance and wherein to the target substance migrates through saidsurface layer and is taken up by said stripping solvents separating thetarget substance from the fluid or mixture.
 13. The capsule forseparating a target substance from a fluid or mixture of claim 12,further comprising a layer of catalyst or enzyme on or in said capsulebody.
 14. The capsule for separating a target substance from a fluid ormixture of claim 12 wherein said stripping solvents are primary,secondary, tertiary, and hindered amines, caustic solutions, ionicbuffer solutions, ammonia, or other solvents having solubility of carbondioxide.
 15. The capsule for separating a target substance from a fluidor mixture of claim 12 wherein said stripping solvents are amines. 16.The capsule for separating a target substance from a fluid or mixture ofclaim 12 wherein said surface layer is made of a porous solid.
 17. Thecapsule for separating a target substance from a fluid or mixture ofclaim 12 wherein said surface layer includes carbon fibers.
 18. Thecapsule for separating a target substance from a fluid or mixture ofclaim 12 wherein said surface layer includes nanotubes.
 19. The capsulefor separating a target substance from a fluid or mixture of claim 12wherein said surface layer is made of any of several families ofpolymers, including polystyrene, polyethylene, polypropylene, and nylon.20. A method of separating a target substance from a fluid or mixture,comprising the steps of: providing capsules having a coating andstripping material encapsulated in said capsules, wherein said coatingis permeable to the target substance; exposing said capsules having acoating and stripping material encapsulated in said capsules to thefluid or mixture, wherein the target substance migrates through saidcoating and is taken up by said stripping material; and separating thetarget substance from the fluid or mixture by driving off the targetsubstance from said capsules.
 21. The method of separating a targetsubstance from a fluid or mixture of claim 20 wherein said step ofproviding capsules having a coating and stripping material encapsulatedin said capsules comprises providing capsules having a coating andstripping solvents that are primary, secondary, tertiary, and hinderedamines, caustic solutions, ionic buffer solutions, ammonia, or othersolvents having solubility of carbon dioxide encapsulated in saidcapsules.
 22. The method of separating a target substance from a fluidor mixture of claim 20 wherein said step of providing capsules having acoating and stripping material encapsulated in said capsules comprisesproviding capsules having a coating and stripping solvents that areamines encapsulated in said capsules.
 23. The method of separating atarget substance from a fluid or mixture of claim 20 wherein said stepof providing capsules having a coating and stripping materialencapsulated in said capsules comprises providing capsules having acoating made of a porous solid and stripping material encapsulated insaid capsules.
 24. The method of separating a target substance from afluid or mixture of claim 20 wherein said step of providing capsuleshaving a coating and stripping material encapsulated in said capsulescomprises providing capsules having a coating that includes carbonfibers and stripping material encapsulated in said capsules.
 25. Themethod of separating a target substance from a fluid or mixture of claim20 wherein said step of providing capsules having a coating andstripping material encapsulated in said capsules comprises providingcapsules having a coating that includes carbon nanotubes and strippingmaterial encapsulated in said capsules.
 26. The method of separating atarget substance from a fluid or mixture of claim 20 wherein said stepof providing capsules having a coating and stripping materialencapsulated in said capsules comprises providing capsules having acoating made of any of several families of polymers, includingpolystyrene, polyethylene, polypropylene, and nylon and strippingmaterial encapsulated in said capsules.
 27. The method of separating atarget substance from a fluid or mixture of claim 20 wherein the targetsubstance is carbon dioxide and wherein said step of providing capsuleshaving a coating and stripping material encapsulated in said capsulescomprises providing capsules having a coating that is permeable tocarbon dioxide and carbon dioxide stripping material encapsulated insaid capsules.
 28. The method of separating a target substance from afluid or mixture of claim 20 wherein the target substance is nitrousoxide and wherein said step of providing capsules having a coating andstripping material encapsulated in said capsules comprises providingcapsules having a coating that is permeable to said nitrous oxide andwherein nitrous oxide stripping material is encapsulated in saidcapsules.
 29. The method of separating a target substance from a fluidor mixture of claim 20 wherein the target substance is sulphates andwherein said step of providing capsules having a coating and strippingmaterial encapsulated in said capsules comprises providing capsuleshaving a coating that is permeable to said sulphates and whereinsulphates stripping material is encapsulated in said capsules.
 30. Themethod of separating a target substance from a fluid or mixture of claim20 wherein the target substance is hydrogen sulfide and wherein saidstep of providing capsules having a coating and stripping materialencapsulated in said capsules comprises providing capsules having acoating that is permeable to said hydrogen sulfide and wherein hydrogensulfide stripping material is encapsulated in said capsules.